Rotary fluid-pressure machine



May 6, 1941. F. M. THOMAS ETAL 2,240,374

ROTARY FLUID-PRESSURE MACHINE I Filed Sept. 6, 1939 4 Sheets-Sheet 1 May'6, 1941. F. M. THOMAS ETAL 2,240,874

ROTARY FLUID'PRESSURE MACHINE Filed Sept. 6, 1959 4 Sheets-Sheet 2 I M O May 6, 1941.

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May 6, 1941. F. M. THOMAS ETAL ROTARY FLUID-PRESSURE MACHINE Filed Sept. 6, 1939 4 Sheets-Sheet 4 V My r CB a a Jon/76', N HI TCH Patented May 6, 1941 UNITED STATES PATENT OFFICE ROTARY FLUID-PRESSURE MACHINE Frederick Metcalt Thomas and Frederick Alexander Nigel Hitch, Hatfield, England, assirnors to The De Havilland Aircraft Company limited, Hertfordshire, England Application September 6, 1939, Serial No. 293,638 In Great Britain September 23, 1938 19 Claims. This invention relates to rotary fluid pressure machines which involve the known principle of displacement of volume by the interengagement of continuous series of teeth of relatively moving wheels and concerns improvements relating to such machines and adaptations of them for various purposes, hereinafter called fluid pressure machines of the gear pump type. A primary purpose is the construction of a form of such a machine, of compact and sturdy design, and constructional simplicity, to give a high output torque at low speed when supplied with an operating fluid under pressure. A particular object is the adaptation of such a machine for changing the .pitch of the blades of a variable pitch airscrew, i. e., to act as a pitch changing motor. A further object of the invention is to construct an epicyclic machine to operate as a hydraulic motor, in which hydraulic loads are uniformly and 'symmetrically applied about an axis. 'In furtherance of this object, in some designs, the hydraulic loads on individual planets in an epicyclic machine used as a motor can be such as to produce practically pure torque on these wheels.

The invention proposes a rotary fluid pressure machine of which the rotors form parts 1 of a compound epicyclic gear.

. in such a manner, that, the ratio between the annulus and planet (or equivalent parts) of one train being different from the corresponding ratio in another train, an epicyclic reduction gear effect is obtainable.

In the particular embodiments of the invention hereinafter described, the compound epivcyclic gear trains include at least one pair of rigidly connected coaxial gear wheels, usually termed planets, the common axis of which revolves about the common axis of two other relatively rotatable gear wheels, each of which meshes with its associated planet or planets. These relatively rotatable gear wheels are termed sun wheels if externally toothed and annuli if internally toothed. For some purposes it is convenient to construct a gear train having both sun wheels and annuli.

In operation a fluid pressure machine constructed according to the invention with planets and annuli only, will run with the member supporting the planet bearings, usually termed the cage, rotating quickly relative to either of the annuli which annuli rotate slowly relative to one another. If one of the annuli is fixed and the machine is supplied with fluid under pressure, mechanical power at high speed and low torque may be takenfrom the cage, or mechanical power at low speed and high torque from the slowly rotating annulus. Alternatively both these members may be loaded to give any desired combination of power outputs within the capacity of the machine. Further, mechanical power may be supplied to either of these members to supplement the power normally available from the other.

It is also within the scope of the invention to supply mechanical power to either or both of these members of the machine in order to drive it as a pump; if power is supplied to one member only, in addition to obtaining hydraulic power output, some power may be taken mechanically from the other member.

A machine built with sun wheels instead of annuliwould lend itself to similar methods of operation whilst a machine with both sun wheels and annuli could be used in an even greater variety of ways.

A further feature of the invention is the incorporation within the mechanism of means for controlling the direction of rotation. In one case, this takes the form of a rotatable distributor valve so arranged that whatever rotary motion is imparted to the valve by any suitable controlling means, is copied exactly by a rotating member, e. g., the cage of the machine With this device, the mechanism acts as a servo motor, following the rotation of the distributor valve, and starting, stopping and reversing, with it. In another case a simple reversing gear is associated with the cage member and forms a particularly convenient means for controlling the mechanism. Both of these mechanisms are easily adaptable to control by speed-sensitive or other types of governor.

The invention includes a variable pitch airscrew having a pitch-changing motor comprising epicyclic gearing with two or more trains, adapted to operate as. a fluid pressure machine of the gear-pump type, and to be controllably supplied with pressure-fluid during running of the airscrew.

The accompanying drawings illustrate several forms of the invention each of which is suitable for embodiment in or association with a variable pitch airscrew, as pitch-changing motor thereof.- 7 Figures 1 and 2 are diagrams illustrating the a compound (two Figure 4 is a sectional axial elevation, half on equivalent to the pitch of one tooth. viz. oneninth of the peripheral length of pinion 3.

Figure 2 can be regarded as a linear development of an epicyclic gear system. In the actual system the racks I and 2 are circular and continuous, usually internally toothed annulus members, and the pinions 3, l,- are mounted for rotation together on a planetaxis which revolves round the axis of the annuli, being mutually supported hy'a revolving cage, or being mounted on a planet axiswhlch'revolves around the annulus axis by virtue of an eccentric bearing element line A-A of Figure 3 and half on line B B of Figure 3. v v V Figure 5 isa partial view, in section on line .X-Xof Figure 7.

Figure is a sectional axial elevation of a motor similar to that illustrated in Figure 7 but not incorporating sun wheels.

Whilst the principle of compound epicyclic reduction gear systems is well known, it may help to clarify the detailed description if we first consider the operation in fimdamental conception,

with the aid of Figures 1 and 2.

In Figure 1, there are represented two racks,

or toothed wheels I and 2 of infinite radius. Each is engaged by pinions 3 and 4 respectively, and for the purposes of this explanation all teeth have the same pitch although this is not necessary in a compound gear. The pinions 3 and l have their axes in a cage element represented by a bar 5. They are deemed to be positively interconnected to rotate together. The numerals in series designate teeth on the racks and tooth spaces of the pinions. The teeth on pinion 3 and pinion l are shown diiferent in number, by one. Now if the pinions be rolled along the rack from left (full line) to right (broken line) in one revolution of pinion 3 its axis travels through a distance equal to the circumference of its pitch circle. At the same time pinion l likewisemakes one revolution-and during its travel on the rack 2 its axis only moves through a distance equal to the circumference of its pitch circle, and accordingly if the racks are relatively fixed the cage bar 5 will take up the angular disposition shown I makes a fluid tight fit on the larger part of the of teeth on pinion 3 and on pinion l. Pinion 3 has nine-teeth, pinion 4 has eight teeth; rack 2 istherefore moved along in the same directionwhich in such cases is rotatable in the opposite sense of direction to the last annulus and planet axis. As will be seen, if the tooth diiference between engaging wheeis is then unitythe eccentric bearing will revolve one turn. backwards for every one-tooth advance of the planet.

To illustrate fundamentally a further matter, in Figure 2 two shaded areas I are shown. These represent what are, in this invention, tooth spaces which receive hydraulic pressure, and they indicate how the gear system can then form a hydraulic motor. The spaces 1 are su lied from a common source of pressure. If the pressure fluid be admitted on the other sides of the pinions, the motion will be reversed. The wall formed by a. member 8 which is fixed with the bar 5, forms a wall of the pressure-space, closely and slidably fitting tops of the teeth of the racks and pinions.

Compound epicyclic motor with one pair of planet wheels Figs. 3, 4, 5

The construction of this machine will now be described. A cylindrically shaped casing I0 is assembled by bolting together appropriate parts. One of these parts supports an internally toothed fixedannulus ll having X+1 teeth, A, of cycloidal form. The casing ll supports, in bearings l2, an output shaft l3. Inside the casing, this shaft l3 carries the driven, second. annulus I. The annulus M has X internal teeth A, also of cycloidal form and the two annuli II, M, are coaxial. In the bearings I5 carried in part of the casing Ill and its extension IIA, and in a bearing l6 within shaft I3 is mounted shaft II with eccentric parts "A. The shaft I! may be extended so that a high speed, low torque output may be taken from it. The part of the shaft between the bearings l5 rotates within an extension part IUA of the casing II for valving purposes to be described.

There are two planets. These are, the first planet It, with X external cycloidal teethim; and the second planet I! similarly toothed with X1 teeth ISA. The planet [8 engages annulus ll; planet J9 engages annulus I. The pair of planets are bolted together with a member 2| and sealing pieces 20A and 20B. The planet wheels and these members are rigidly mounted on the bush 22, which is borne, 'by bearings 2|, for rotation on the. eccentric "A. This bush eccentric,

In the casing extension "A is an inlet duct 23 for admitting the working fluid and an outlet duct 24 for its exhaust. These ducts are always open to annular channels 23A, 24A, respectively, formed inthe shaft H. The channels communicate by internal bores 23B, 2413, to distributor valve chest spaces 23C, 24C, formed respectively are ducted by ducts 26 and 21 which lead to the spaces between the teeth of the planets. The ducts 26 run to the spaces between the teeth NBA, and ducts 21 run to the spaces between the teeth ISA. The lands 25 act as valve faces, which in the course of rotation of "A relative to 20 and 22, consecutively and progressively open the chest 23C (and thus the fluid supply) to about half the tooth spaces; and likewise open the other chest 24C (and the exhaust) to the other spaces. The lands 25 being diametrically arranged, it follows that the hydraulic fluid is supplied under pressure to one half of the total tooth spaces and drained from the other half, so causing a relative motion between the annuli and the planets. It will be seen that the only fluid communication between the pressure spaces in one train I4, I9, and the other train, II, I8, is that which is mutual with the valve chest spaces 23C, 24C, and therefore with the entry and egress.

Direct leakage from the pressure spaces to the drain spaces is prevented by the sealing properties peculiar to pairs of co-operating internally and externally toothed cycloidal rotors in which the externally toothed rotor has one tooth less than the internally toothed rotor.

In the position shown in Figure 4, the resultant hydraulic thrust on the planet wheels rocks them about the point Z (the instantaneous point of coincidence of the pitch circles of the annulus II and the planet wheel I8) so causing a slow rotation of the output annulus I4, about the instantaneous centre Z. As the planet wheels rock, the eccentric HA is rotated in the opposite sense to their direction of rocking. This causes the lands 25 always to take up their optimum phase position so making the motion continuous. This backwards rotation of the eccentric is at a relatively high speed, being in fact one complete turn for every cycle of tooth engagement between the teeth I IA and I8A and is X times as fast as the rotational speed of the output member I3. Of course the numbers of teeth on the two planet wheels may differ by any number greater than unity for obtaining different gear ratios.

Compound epicyclic motor with one pair of planet wheels incorpo ating a servo cntrolFig. 6

In Figure 6 there is illustrated what is, in effect,

a modification of the arrangement shown in Figures 3, 4, 5. In this form part of the valving system is in the periphery of the fixed annulus and a servo control is incorporated.

The parts referred to at I00 constitute a casing which is of generally cylindrical form. Within piece IMA and to a second planet wheel I05,

these members constitute a planet wheel assembly which is rotatably mounted by bearings I06 on the eccentric part of the shaft I01; the two planet wheels have different numbers of teeth, and are rigid together.

The shaft I01 is borne within the member I02 and in the casing I00, by bearings I09. The middle part of the shaft I01, between the bearings I06, is formed with an eccentric distributor element III which has two arcuate channels M in it, each subtending nearly 180 of angle,

and which is otherwise ablose rotatable fit in the planet wheel bores. Each planet wheel has radial ducts H03, 00 between every pair of teeth which communicate with the channels 0A. The lands left between the adjacent ends of the channels prevent fluid communication from one channel to the other. Mounted upon a cylindrical boss II2 on the shaft I01 within one end of the casing I 00, and coaxial with the main axis of this shaft, is a distributor valve II3. This distributor valve is rotatable in the casing in bearings II4. It is also partly rotatable on the boss II2, through an angle limited by a dog II5, projecting inwardly from the distributor element II3 into a peripheral slot or recess Il2A,

.formed in the boss H2, or other convenient means.

The valve element I I3 has a nearly semicircular inlet valve channel IIG formed in it peripherally and a second nearly semicircular outlet channel I I1, these being separated by lands between their ends. The channel H6 is axially longer (1 .e., is a wider channel) than channel II1. In the casing I00, at H8, is an inlet duct supplied from a source of pressure fluid. This duct II8 leads into an internal supply-groove II8A which is so placed that it is always open to channel IIG, but never to channel II1. In the valve element H3 is or are a duct or ducts II9, which educt liquid to the outside from channel I I1. The distributorvalve II3 also contains one or more radial ports I2I, which, when the distributor valve is at the mid-position of its travel, as determined by the engagement of the dog I I5 in the slot I I2A, communicates with a radial port or ports I2 IA in the end I I2 of the shaft I01.

By means of an axial bore in the shaft I01, the ports I 2IA are permanently connected to the outside of the machine. In the casing I00 are ducts I20 leading to the tooth-spaces of the first annulus IOI. In the planet I04 are ducts 03 from each tooth-space to communicate with either channel I IOA (above described) and in the planet I05, similar ducts IIOC likewise communicating.

The functioning of the machine is as follows:- when the distributor valve H3 is in its mid position on the shaft I01, the fluid will flow from the annular groove II 8A to the half annulus H6, thence through the ports I2I and I2IA to drain. In this position of the distributor the motor will not rotate. If the distributor H3 is now turned; far enough in one direction relatively to the shaft I01, the radial ports I2I will no longer communicate with the corresponding ports I2IA, and the fluid will flow through approximately half of the ducts I20 to fill the tooth spaces in one half of the fixed annulus I0 I.

By means of half of the ports 03 and H00 and one of the grooves IIOA, the corresponding tooth spaces of the moving annulus I03 will also simultaneously be filled with fluid under pressure. The pressure acting on the same side of both the planet wheels will .cause the machine to rotate, the shaft I01 moving quickly and the shaft I02 slowly. Fluid will be exhausted through the other half of the ports 00 and H03, passing through the other groove IIOA and thence by means of the remaining ducts I20 and the half annulus 1 to drain through the ports IIS. Thus as long as the distributor valve II3 is rotated at the same speed as the shaft I01, the motor will continue to rotate; should the distributor valve be stopped relative to the casing I00 (i. e., moved relatively to the shaft I01) the motor will rotate until the ports I2IA come into alignment with the ports l2l, when the motor will stop. Rotation of the valve relative to the casing in either direction will result in the motor following the valve in that direction. -Hence any movement given to the distributor valve H3 results in a similar movement of the shaft I01 and a correspondingly smaller angular move- Compound epicyclic hydraulic motor having three pairs of planets cooperating with both sun wheels and annuli. Figs. 7, 7A, 8, 9

In order to afford large volumetric capacity and balanced hydraulic loads, and to avoid having to provide balance weights on the central shaft and to secure a more symmetrical design, it is sometimes preferable to construct a machine with more than one pair of planet wheels. When this is done the planet wheels have many teeth less than the number on the annuli so that the advantage of the sealing properties peculiar to the combinations of cycloidal wheels described above, are lost, and it isnecessary to provide an hydraulic abutment member rotating with the axes of the planet wheels. Such an embodiment will now be described with reference to Figs. '7, 7A, 8, and 9. Although involute teeth are shown in Figure 8, the type of tooth profile is not of fundamental importance in this particular embodiment. Figure '7 shows a cross section of this type of motor adapted for changing the pitch of the blades of a variable pitch airscrew and controlled by a simple formof reversing mechanism.

403. The cage is further borne by bearing 333 in the member 33. The centre piece, held between the two side plates 40 and 403, has segmental blocks 40C integrally formed thereon. The segmental blocks 400 are shaped so as to fit nicely in the spaces between the annulus, planet, and sun wheels of each stage so as to prevent the leakage of fiuid past the tops of the teeth of these wheels. Each planet 4| meshing with the fixed annulus 3|, is rigidly fixed to the corresponding planet'wheel 42, meshing. with the moving annulus 34, and the three pairs of rigidly connected planets are mounted on spindles 43 in the cageassembly. The planets 4| all engage sun-wheel 44 and the planets 42 engage sun-wheel 45.. These sun-wheels 44, 45, are

mounted for independent of the annuli 3|, 34.

The annuli, planets, and sun wheels are proportioned so that the complete system constirotation about the'axis tutes what may be termeda high-ratio reduction gear-motor. The ratio of the number of teeth on the planet 4|, to the number on the annulus 3|, is different from theratio of the number of teeth on the planet wheel 42, to the number on the annulus 34. Upon rotation of the cage 40, the planets roll in the annuli and they therefore rotate relative to the cage.

mesa

As however the planets are fixed together in pairs, the annulus 34 is slowly rotated relative to the fixed annulus 3|. Incidentally the sun wheels rotate at different speeds. When this motion is produced by supplying fluid pressure as hereinafter described, airscrew blades such as '41, having driven bevel pinions 46 engaging with bevel pinion 33A, can be rotated for pitch changing.

The epicyclic gear system above described forms a hydraulic motor in which hydraulic energy is converted into mechanical energy. It will be seen from Figure 8 that a series of ducts lead from the blocks 40C to the working spaces between the wheels. Each planet 42, cooperating with the teeth 34A of the annulus 34, and the teeth of the sun-wheel 45, and with the walls of adjacent blocks 40C and the axially spaced walls of the cage assembly, has four working spaces disposed around it, viz, 42A, 42B, 42C, 42D. In' one running direction (1. e., with planets 42 rotating counter-clockwise, and with their axes and the cage revolving clockwise about the axis of the annuli, and sun wheel 45 rotating clockwise, and annulus 44 rotating in a direction depending upon the relative ratios between the planets and annuli of the two halves of the train), the spaces 42C, 42D, are pressure spaces, and spaces 42A, 42B, are connected to exhaust. Each train of five gears has six pressure spaces and six drain spaces in it, the total for the motor being twelve pressure spaces and twelve drain spaces at any one time, all the corresponding spaces of both trains being hydraulically in parallel. On account of the large number of pressure spaces, and the large number of turns of the planets in the cage for each turn of the annulus 33 relative to the annulus 3| a very high torque can be obtained from the member 33 for a. comparatively low hydraulic pressure. Moreover, the distribution of pressures and forces is symmetrical throughout the system. 1

With regard to the distribution of the fluid in this construction, it will be seen that the ports opening into the spaces 42A--D are connected to axially directed ducts 50 in the centre piece 40A. These run through the cage assembly and similar ducts from them lead to the corresponding working spaces in the other train of gears. Since each block has four ducts 50, there are twelve'ducts in all. The end of the cage assembly approximately within the bearing 30A has a cylindrical coaxial bore, which is a close running fit upon a sleeve 5l,.flxed to and surrounding a valve element 52. The element 52 is of generally cylindrical form and, is rotatably supported by a bearing 52A in the cage element 40, and by a bearing 523 in the casing 30. The valve element 52 is formed with axially directed deep channels 52C, constituting transfer distributor ports. These are twelve in number, and are connectable withthe ducts 50 through holes in the sleeve 5| (sectioned in Figure 9). The twelve channels consist of. six long and six short channels alternately spaced, each long channel communicating with the annular groove 52D permanently open to drain. The shorterchannels are permanently in communication with the annular groove 53 formed in the casing 30; Groove 53 is connected to a pressure source through "A, and also to a pressure relieving valve 54 which can allow escape'to the outside. A cylindrical element 56 is keyed to the cage element 403, at 56A. This element 56 carries the sun-wheel bearings.

At its forward end, the member 56 is formed with a number of axially directed slots 51A. The part of the valve element 52 which surrounds these slots is provided with a number of corresponding slots 513, which are of helical form, see Figure 7A. Slidably mounted in the member 56, is a piston 58 carryingpins supporting pairs or rollers 51, arranged so that one roller of each pair operates in the axial slot of the member 56 while the other roller of each pair operates in a helical slot of the member 52. The slots are formed so that when piston 58 is moved its full amount in the member 56, the valve element 52 is rotated through one twelfth of a turn relative to 56, and hence relative to the cage assembly 40.

and only three short and three long channels in its distributor valve.

General remarks As stated previously, each of the machines .above described has two members, l3 and I! in Figure 3, I02 and I0! in Figure 6, 33A and 56 in Figure 7, so geared that when the machines are running, the members I3, l02-and 33A rotate very slowly relative to the members i1, I01, 56, respectively. Although the functioning of the machines have been described when operating as hydraulic motors with mechanical power taken With the piston in its forward position as shown in Figure 7, the short channels 520 will register with ends of alternate ducts '50, while the long channels will communicate with the ends of the other ducts 50. When the piston is fully displaced to its rear-most position the short channels will register with the ducts previously regis tering with the long channels and vice versa. This alternative registration constitutes a means for reversing the motor. The movement of the piston 58 may be controlled in any convenient manner, for example, by enclosing it within a cylinder 58B rigidly attached to member 56, and supplied with operating fluid through a conduit 55, the return stroke being effected by the compression spring 58A.

If the pins 51. and the straight and helical slots are omitted; by providing means such as a pin 563 on the shaft 56, working in a slot 560 in the valve element 52 so as to allow the valve to rotate by only one twelfth of a turn on the shaft 56, a

servo interconnection between the valve and the" cage will be obtained. That is, as long as the valve 52 is rotated, the cage assembly 46 will copy its motion: and when the valve 52 is stopped the cage will rotate through a further one-twentyfourth of a turn, until the mid position of registration of the channels 520 and the ducts 50 is reached, when the motor will also cease to rotate.

As in the case of theservo control of the motor illustrated in Figure 6, it is necessary for the porting to be so designed that the cage rotates in the same direction as the initial direction of rotation of the distributor valve.

Compound epicyclic motor similar to that illustrated in Fig. 7 but not incorporating sun wheels. Fig. 10

In this construction the sun wheels are not incorporated, and the centre part 94 of the cage assembly is shaped as indicated in Figure 10, so as to form an oil tight seal round the greater part of the peripheries of the planet and annulus wheels.

There are six working spaces which exist in each set of four wheels making a total of twelve spaces for the whole motor. Thus for a given oil pressure, a motor of this form will give approximately half the output torque given by a motor of the same size and gear ratio which incorporates sun wheels. On the other hand there are considerably more teeth hel ing to prevent leakage over the periphery of the planet wheels between the working spaces. The functioning of the mach e is eriera wsimilar to that illustrated in Figure 7, and the direction of fluid flow for one direction of rotation is indicated by the arrows on Figure 10. Such a machinewill have only six ducts, at 96A and 963, leading to those in the part corresponding to the cage member 40 from their low speed members, it is within the scope of this invention to take power from either or both of the shafts, or to take power from one while some power is supplied to the other. Similarly, if the machines should be required to operate as pumps, it is within the scope of the in- ,vention to drive either or both shafts, and in those cases where only one shaft is driven, to take some power from the other shaft if desired.

Also, although the above description has referred to machines having straight teeth with either cycloidal or involute profiles, it is to be understood that helical or double helical teeth may sometimes be used with advantage, and that except for the machines having planets with one tooth less than the number on the cooperating annuli, in which 'case straight cycloidal or helical cycloidal teeth are necessary, any suitable tooth rofiles may be used.

Again the invention is not limited to gear trains having the axes of all the wheels parallel, but may be applied to trains built with bevel gears.

It will be seen that if several output or input members rotating at different speeds should be required, a motor could be constructed to fulfil this purpose. Such a machine, is also included within the scope of this invention.

ferred at present, and form subordinate features of this invention.

It is also to be understood that the foregoing description leaves to the ordinary skill of the art, such questions as the provision of appropriate glands and the proper fitting of the parts to receive suflicient fluid-tightness, tooth ratios, and the like. the description having been confined to essentials and not concerning itself with constructional detail. to which an understanding of the operation of the machine will naturally guide the designer.

What we claim is:

1. A fluid pressure machine of the gear pump type; comprising a. plurality of epicyclic gear trains arranged side by side and interconnected for conjoint rotation, the tooth spaces of each train constituting pressure compartments for driving fluid. ductsfor supplying driving fluid under pressure to the tooth spaces of the gear trains and for removing such fluid therefrom, nartition means between the juxtaposed gear trains sealing the adjacent ends of the tooth s aces thereof against intercommunication of fluid under pressure directly from the end of a tooth space of one gear train to the end of a tooth space of the juxtaposed gear train, and means effecting a fluid-tight seal for the ends of the tooth spaces on each side of the gear train assembly.

pressure to such tooth spaces of each gear train and for thereafter removing fluid from such spaces, and said pressure fluid distributing means including an element movable to interrupt simultaneously communication between said supply and discharge conduits and the tooth spaces of said gear trains for discontinuing rotation thereof.

3. A fluid pressure machine of the gear pump type, comprising apair of epicyclic gear trains arranged side by side, each gear train including an internally toothed annulus and an eccentrically mounted, externally toothed planet having one less tooth than its corresponding annulus, theteeth of both annulus and planet being'of generally cycloidal shape and mutually disposed to form of the tooth spaces pressure compartments for driving fluid, and the planet gears of the two trains being rigidly and coaxially connected to each other for conjoint rotation, and distributing means for fluid under pressure communicating with the tooth spaces of both gear trains for supplying such fluid simultaneously to all the tooth spaces in substantially one half of for driving fluid, and the planet gears of the two trains being rigidly and-coaxially connected to each other for conjoint rotation, partition means 4 between the juxtaposed gear trains sealing the adjacent ends of the tooth spaces thereof against intercommunication of the fluid under pressure directly from the end of a tooth space of one gear train to the end of a tooth space of the juxtaposed gear train means effecting a fluid-tight seal for substantially the other half of each gear train,

each gear train, and for removing such fluid from all the tooth spaces in substantially the other half of each gear train.

4. A fluid pressurermac hine of the gear pump type, comprising a pair of epicyclic gear trains arranged side by side, each gear train including an internally toothed annulus and an eccentri- .cally mounted externally toothed planet having one less tooth than its corresponding annulus, the

' teeth of both annulus and planet being of generally cycloidal shape and mutually disposed to form of the tooth spaces pressure compartments for drivingfluid, and the planet gears of the two gear trains being rigidly and coaxially connected to each other for conjoint rotation, one

of the gears of each train having therein ducts communicating in a generally radial plane one with each tooth space of the train, and distributing means for fluid under pressure communicating with said ducts for supplying such fluid simultaneously to all such ducts in substantially one hali of each gear train, and for removthe other half of each gear train.

5. The fluid pressure-machine of claim 4, an'd valve means rotatable with respect to the gear trains for reversing the direction of flow through the fluid distributing means, thereby to reversethe direction of relative rotation between the Q planet and annuli of the gear trains.

and means for driving said fluid distributing,

means in synchronismwith the rotation of said gear trains, for changing continually the distribution of fluid under pressure to the tooth spaces of said gear trains and removal of fluid therefrom in accordance with the change in phase relationship of the internally toothed annuli and the externally toothed planets.

7. A compound epicyclic gear fluid pressure machine of the gear pump type, comprising relatively rotatable annuli, planets respectively engaging said annuli, positive interconnection means between respective planets to insure rotation thereof together for the transmission of torque from one annulus to another, means including teeth of mutually engaged planet and annulus wheels to fornr closed pressure spaces therebetween, a rotatable planet supporting element, and rotary distributor valve means r0- tatable independently of said planet-supporting element. x

. 8. A compound epicyclic gear fluid pressure.

- tation thereof together for the transmission of ing such fluid from all the ducts in'substantially 6. A fluid pressure machine of the gear pump type, comprising a pair of epicyclic gear trains arranged side by side, each gear train including an internally toothed annulus and an eccentrically mounted, externally toothed planet having one lesstooth than its corresponding annulus, the

teeth of both annulus and planet being of generally cycloidal shape and mutually disposed to form of the tooth spaces pressure compartments torque from one annulus to another, means including teeth of mutually engaged planet and annulus wheels to form closed pressure spaces therebetween, a rotatable planet supporting element, and rotary valve means rotatable with said planet-supporting element and adjustable as to phase position relatively thereto for the purpose of controlling and reversing the supply and delivery.

9. A compound epicyclic gear fluid pressure machine of the gear pump type, comprising relatively rotatable annuli, planets respectively engaging said annuli, positive interconnection means between respective planets to insure rotation thereof together for the transmission of torque from one annulus to another, means including teeth of mutually engaged planet and to said first annulus, a corresponding plurality of toothed planets engaging said second annulus, means positively interconnecting each first planet with its correspondent second planet for mutual rotation, cage means supporting all said planets for rotation about their own axes and for revolution of their axes about the annulus axis, axially spaced elements enclosing toothspaces of the first annulus and first planet, and second annulus and second planet, said elements also separating the respectively enclosed spaces, and wall parts of said cage means together with said spaced elements and each respective annulus and planet forming pressure spaces for the operation of the machine as a whole as a motor fluid pressure ma chine of the gear pump type.

11. A machine according to claim 10, in which said first planets a-ll engage a first toothed sun wheel, said second planets all engage a second sun wheel, said sun wheels are mounted coaxially and for relative rotation, and further pressure spaces are afiorded by the respective planets and sun wheels together with the cage element and axially spaced elements.

12. In propeller pitch changing mechanism, a

, member rotatable in opposite directions for increasing and' for decreasing the propeller pitch respectively, a plurality of epicyclic gear trains arranged side by side and interconnected for concentric rotation, the tooth spaces of each train constituting pressure compartments for driving fluid, driving fluid distributing means communicating with the tooth spaces of the gear trains for supplying fluid under pressure to such spaces and for removing such fluid therefrom, for effecting very slow rotation of said member. and reversing means operable to control the flow of fluid under pressure through said distributing means for changing the direction of rotation of said gear trains, in turn to reverse the direction of rotation of said member.

13.. A fluid pressure machine of the gear pump type, comprising a pair of epicyclic gear trains arranged side by side and interconnected for conjoint rotation, the tooth spaces of each train constituting pressure compartments for driving fluid,

gear train, and said partition means being apertured generally axially of said gear trains for flow of fluid from the zone of the gear train nearest to said pressure fluid distributing means to the zone of the gear train remote therefrom, and for return flow of fluid from the zone of the latter gear train to the zone of the former and thence back to said fluid distributing means.

15. The fluid pressure machine of claim 14, wherein the partition means is flxed to one of the gears of the gear trains.

16. A fluid pressure machine of the gear pump type, comprising a plurality of epicyclic gear trains arranged side by side and interconnected for conjoint rotation, the tooth spaces of each train constituting pressure compartments for driving fluid, a supply conduit for fluid under pressure, a discharge conduit for fluid, and fluid distributing means interposed between said fluid supply and discharge conduits and the tooth spaces of said gear trains, and rotatable with respect to said gear trains to effect delivery of fluid under pressure to the tooth spaces for impelling rotation of the gear trains in the direction in which said distributing means was rotated, and

. further operable to stop supply of fluid under a supply conduit for fluid under pressure and a discharge conduit for fluid, and pressure fluid distributing means disposed generally coaxially with said gear trains betwen them and said fluid supply and discharge conduits, having therethrough ducts communicating between said conduits and the tooth spaces of both gear trains, both for supplying fluid under pressure to such tooth spaces of each gear train and for thereafter removing the fluid from such spaces, and said pressure fluid distributing means being rotatable with respect to both gear trains for alter- 4 ing the fluid ducts to effect simultaneous reversal of rotation of both of said gear trains.

14. A fluid pressure machine of the gear pump type comprising a pair of epicyclic gear trains arranged side by side and interconnected for conjoint rotation, the tooth spaces of each train constituting pressure compartments for driving fluid, a supply conduit for fluid under pressure and a discharge conduit disposed both at one side of said pair of gear trains, pressure fluid distributing means disposed generally coaxially with said gear trains, between them and said fluid supply and discharge conduits, and having therethrough ducts communicating between said conduits and the gear train nearest to them, partition means between the juxtaposed gear trains sealing the adjacent ends of the tooth spaces thereof against intercommunication of fluid under pressure directly from the end of a tooth space of one gear train to the end of a tooth space of the paired pressure to the tooth spaces of said gear trains upon rotation thereof through an angle corresponding to the rotation of said distributing means.

17. A fluid pressure machine of the gear pump type, comprising a pair of epicyclic gear trains arranged side by side and interconnected for conjoint rotation, the tooth spaces of each gear train constituting pressure compartments for driving fluid, ducts for supplying driving fluid under pressure to the tooth spaces of the gear train and for removing such fluid therefrom, a cage element rotatably supporting the planet gears of both gear trains within the coaxia'lly disposed annuli, said cage element being itself rotatable about the axis of the annuli, and a wall carried by said cage element interposed between the adjacent sides of the planets and pinions and sealing the ends of the tooth spaces of such sides against intercommunication of fluid under pressure directly from the end of a tooth space of one gear train to the end of a tooth space of the other gear train.

18. A fluid pressure machine of the gear pump type, comprising a plurality of epicyclic gear trains arranged side by side and interconnected for conjoint rotation, the tooth spaces of each train constituting pressure compartments for driving fluid, a cage element rotatably supporting the planet gears of both gear trains within the coaxially disposed annuli, said cage element being itself rotatable about the axis of the annuli, a wall carried by said cage element interposed between the adjacent sides of the planets and pinions and sealing the ends of the tooth spaces of such sides against intercommunication of fluid under pressure directly from the end of a tooth space of one gear train to the end of a tooth space of the other gear train, and fluid distributing means for supplying driving fluid under pressure to the tooth spaces of the gear trains and for removing such fluid therefrom mounted on said.

cage element for rotation therewith.

19. A fluid pressure machine of the gear pump type, comprising a pair of epicyclic gear trains arranged side by side and interconnected for conjoint rotation, the tooth spaces of each train constituting pressure compartments for driving fluid, a cage element rotatably supporting the planet gears of both gear trains and mounted rotatably with respect to the annular gears, a source of driving fluid under pressure, and fluid distributing means operable to afford communication for fluid from said source to said gear trains, supported for rotation with said cage. element, but rotatable with respect to such cage element at will to interrupt communication between the fluid source and said gear trains to prevent ro- 

